‘I thought it was the bleakest thing I’d ever read.’ Kenneth Branagh looks slightly astonished as he recalls seeing the script for ‘An Event in Autumn’, which opens the third series of ‘Wallander’. It’s quite a statement from a man used to psychological trauma in and out of character, having fended off the tabloids as his marriage broke up, played Chekhov’s Ivanov and directed Keanu Reeves in ‘Much Ado About Nothing’. And that’s to say nothing of the previous two series, in which Henning Mankell’s Swedish copper endured a gradual breakdown and the death of his father.

But Branagh is in buoyant mood today, chatting happily about his recently announced knighthood (‘in shock’, ‘lovely’, ‘overwhelming response’ and so on) and about his doubts over the severity of the show. ‘Can we really put this out on a Sunday night?’ he wonders. Even so, the tone is optimistic, even hopeful at the outset. Kurt Wallander is attempting to start afresh, moving into his dream house by the sea with a new family. He even cracks a smile. Then a severed limb washes up on the shore and his dog digs up a skeleton in the back garden – normal service resumes. And when a misjudgment puts a colleague in danger, the detective is haunted by the dreadful consequences. ‘It’s a difficult part to play,’ says Branagh. ‘Quite wearing. You feel very thin-skinned and it’s a very raw 90 minutes.’ Mankell’s evocation of ‘Ancient Greek drama, where everything is purified,’ feels apt; this is unusually primal territory for the small-screen policier.

Indeed, the 2008 series of ‘Wallander’ opened the floodgates for ‘The Killing’, ‘The Bridge’, et al. ‘They [viewers] seem to like battered, thinking, feeling people coming up against crime and everything it embodies,’ Branagh reckons, before developing his theory about the enduring appeal of Nordic noir. ‘Watching Sarah Lund do a lot of thinking over 20 episodes of ‘The Killing’… But maybe she doesn’t – maybe she’s in a wonderful neutral place and we do all the thinking. We’re more active as a result of this Scandinavian neutrality.’ TV that makes the viewer work a little harder, in other words. The plot mechanics of the whodunit may be familiar, but the manner of its telling is distinctive. The darkness is complementary rather than self-conscious, the seriousness measured rather than self-parodic, the landscapes used to reflect its characters rather than distract from them. These are balances that aren’t as easy to strike as they sound.

Branagh hopes there will be one more series, climaxing with a two-part adaptation of Mankell’s final, emblematically titled Wallander book, ‘The Troubled Man’. Unless, that is, the author breaks his pledge and writes more. Mankell concedes that, unlike John Le Carré – who declared himself unable to write more George Smiley books because Alec Guinness had taken over the character – Branagh’s Wallander has only stoked the creative fires further: ‘he gives me an insight into so many things I didn’t know about the character,’ says the Swedish writer. That Wallander, like Saga Noren in ‘The Bridge’, may be on the Asperger’s spectrum, for example. ‘Wallander doesn’t really do banter,’ says Branagh. ‘Not only does he not care what other people think, he can’t do anything about it.’

Branagh himself, however, seems content to mix the ‘wearing’ roles with more crowd-pleasing directorial work in the wake of ‘Thor’. But, while he beams about preparing to direct ‘Star Trek’s Chris Pine in a reboot of Tom Clancy’s Jack Ryan stories, his immediate ambitions are somewhat earthier and closer to home. ‘After all this [‘Wallander’], I’d be happy to watch some “Carry On” films.’